The primary sequences of nucleic acids are crucial for understanding the function and control of genes and for applying many of the basic techniques of molecular biology. In fact, rapid DNA sequencing has taken on a more central role after the goal to elucidate the entire human genome has been achieved. DNA sequencing is an important tool in genomic analysis as well as other applications, such as genetic identification, forensic analysis, genetic counseling, medical diagnostics, and the like. With respect to the area of medical diagnostic sequencing, disorders, susceptibilities to disorders, and prognoses of disease conditions, can be correlated with the presence of particular DNA sequences, or the degree of variation (or mutation) in DNA sequences, at one or more genetic loci. Examples of such phenomena include human leukocyte antigen (HLA) typing, cystic fibrosis, tumor progression and heterogeneity, p53 proto-oncogene mutations and ras proto-oncogene mutations (see, Gyllensten et al., PCR Methods and Applications, 1: 91–98 (1991); U.S. Pat. No. 5,578,443, issued to Santamaria et al.; and U.S. Pat. No. 5,776,677, issued to Tsui et al.).
Various approaches to DNA sequencing exist. The dideoxy chain termination method serves as the basis for all currently available automated DNA sequencing machines. (see, Sanger et al., Proc. Natl. Acad. Sci., 74: 5463–5467 (1977); Church et al., Science, 240: 185–188 (1988); and Hunkapiller et al., Science, 254: 59–67 (1991)). Other methods include the chemical degradation method, (see, Maxam et al., Proc. Natl. Acad. Sci., 74: 560–564 (1977), whole-genome approaches (see, Fleischmann et al., Science, 269, 496 (1995)), expressed sequence tag sequencing (see, Velculescu et al., Science, 270, (1995)), array methods based on sequencing by hybridization (see, Koster et al., Nature Biotechnology, 14, 1123 (1996)), and single molecule sequencing (SMS) (see, Jett et al., J. Biomol. Struct. Dyn. 7, 301 (1989) and Schecker et al., Proc. SPIE-Int. Soc. Opt. Eng. 2386, 4 (1995)).
PCT Application No. US99/29584, filed Dec. 13, 1999, and incorporated herein by reference, discloses a single molecule sequencing method on a solid support. The solid support is optionally housed in a flow chamber having an inlet and outlet to allow for renewal of reactants that flow past the immobilized polymerases. The flow chamber can be made of plastic or glass and should either be open or transparent in the plane viewed by the microscope or optical reader. Electro-osmotic flow requires a fixed charge on the solid support and a voltage gradient (current) passing between two electrodes placed at opposing ends of the solid support. The flow chamber can be divided into multiple channels for separate sequencing.
Much more recently, PCT Application No. US00/13677, filed May 18, 2000, discloses a method of sequencing a target nucleic acid molecule having a plurality of bases. The temporal order of base additions during the polymerization reaction is measured on a molecule of nucleic acid. The activity of a nucleic acid polymerizing enzyme on the template nucleic acid molecule is thereafter followed in time. The sequence is deduced by identifying which base is being incorporated into the growing complementary strand of the target nucleic acid by the polymerizing enzyme at each step in the sequence of base additions. The steps of providing labeled nucleotide analogs, polymerizing the growing nucleic acid strand, and identifying the added nucleotide analog are repeated so that the nucleic acid strand is further extended and then sequenced.
In addition, U.S. Pat. No. 4,979,824, describes that single molecule detection can be achieved using flow cytometry wherein flowing samples are passed through a focused laser with a spatial filter used to define a small volume. Moreover, U.S. Pat. No. 4,793,705 describes a detection system for identifying individual molecules in a flow train of the particles in a flowcell. The patent further describes methods of arranging a plurality of lasers, filters and detectors for detecting different fluorescent nucleic acid base-specific labels.
Single molecule detection on solid supports is described in Ishikawa, et al. Jan. J. Apple. Phys. 33:1571–1576. (1994). As described therein, single-molecule detection is accomplished by a laser-induced fluorescence technique with a position-sensitive photon-counting apparatus involving a photon-counting camera system attached to a fluorescence microscope. Laser-induced fluorescence detection of a single molecule in a capillary for detecting single molecules in a quartz capillary tube has also been described. The selection of lasers is dependent on the label and the quality of light required. Diode, helium neon, argon ion, argon-krypton mixed ion, and Nd:YAG lasers are useful in this invention (see, Lee et al. (1994) Anal. Chem., 66:4142–4149).
A need currently exists for more effective and efficient compounds, methods, and systems for single molecule detection, especially as they relate to single molecule DNA sequencing. These and further needs are provided by the present invention.